1. Field of the Invention
The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, the exhaust gas purifying apparatus capturing exhaust particles in exhaust gas.
2. Description of Related Art
Recently, in a compression ignition diesel engine (internal combustion engine) system using light oil, exhaust particles in exhaust gas are captured by a collector provided in an exhaust passage (exhaust system). The collector includes porous partition walls, and the exhaust particles are captured when the exhaust gas flows through the partition walls.
When an accumulation amount of the exhaust particles captured in the collector becomes excessively large, a back pressure of the internal combustion engine is increased due to a resistance for communication in the collector. Thus, a temperature of the collector is increased at proper timing to burn (combusts) the captured exhaust particles. Therefore the collector is regenerated. In this case, if the collector is regenerated in a state where the exhaust particles are excessively captured (accumulated), the temperature of the collector may become very high (e.g., 1500° C.) because the exhaust particles are rapidly burned. As a result, the collector may be broken.
In Japanese Unexamined Patent Publication No. 2004-286019 corresponding to U.S. Pat. No. 6,966,178, the accumulation amount of the exhaust particles is estimated based on a differential pressure across the collector by using an accumulation characteristic. Then, the collector is regenerated when an estimated value of the estimated accumulation amount exceeds a predetermined value. Here, the accumulation characteristic defines a relation between the accumulation amount of the exhaust particles and the differential pressure.
However, in an apparatus disclosed in Japanese Unexamined Patent Publication No. 2004-286019, the accumulation amount may be disadvantageously underestimated under a certain condition in a state where the accumulated exhaust particles are burned so that the accumulation amount is decreased. In the disclosed apparatus, the accumulated amount is estimated based on the accumulation characteristic. If the accumulation amount is once underestimated, the exhaust particles may be accumulated excessively by a time where the estimated value of the exhaust particles increases to reach the predetermined value. Thus, when the collector is regenerated, the exhaust particles are excessively rapidly burned so that the collector may disadvantageously be broken.